There is a clear and continuing need for a thermal protection system (TPS) for a re-entering vehicle (RV) that can withstand heating from a high speed entry or re-entry into an atmosphere of a planetary body that is adaptable enough to accommodate human missions and robotic missions. RV surface heating has two primary sources (1) convective heating (proportional to (velocity)3)from flow of hot gases past the surface and from chemical combination reactions in the gases; and (2) radiation heating (approximately proportional to (velocity)8) from a shock wave that forms preceding the RV).
During high speed initial atmospheric entries, as much as 90 percent of the surface heating can arise through radiation from a reacting shock layer. Where a substantial part of this radiation can be reflected from a heat shield, and prevented from contacting or directed away from the RV surface, the overall heat load can be reduced accordingly, which allows reduced heat shield mass and corresponding greater payload mass for the re-entrant vehicle. Where a TPS can be developed that withstands a large portion of the convective and radiative heating encountered during a high velocity planetary entry, the risk for a crewed mission is reduced, and shorter transit times and higher re-entry velocities, exceeding 15 km/sec (33,651 mi/hour), can be used.
Radiative heating of an RV and its heat shield peaks early in a re-entry interval into an atmosphere, and this heating often arises from specific, limited ranges of wavelengths of concern, {λrad}, dependent upon atmospheric composition, as indicated in FIG. 1. Provision of a heat shield that has an approximately periodic structure that is preferentially reflective for wavelengths in the range {λrad} would reduce the fraction of radiation that contacts the RV surface. However, construction of such a heat shield is likely to be expensive and technically demanding. Preferably, the primary heat shield material is refractory and has a high phase change temperature for ablating.